A collimator shapes and/or blocks electromagnetic energy projected from an X-Ray source. The collimator restricts electromagnetic energy to a size that is smaller than or equal to an active area of an X-Ray detector upon which the electromagnetic energy is projected. Collimation is useful in one example, to eliminate X-Ray irradiation of a part of a patient's anatomy which does not need to be imaged but may fall on the active area of the detector.
A part of an X-Ray collimator that attenuates the X-Ray projection is typically fabricated from an element with a high atomic number, such as lead or tungsten. The attenuating part typically has a blunt profile. The X-Ray projection on the detector may have a very sharp and abrupt transition from the area attenuated by the collimator which provides near complete blocking of the X-Ray, at a near zero signal level, to the area that is not attenuated by the collimator. In particular, the lack of attenuation is particularly stark in areas where there is no patient anatomy to attenuate the X-Ray projection.
The sharp and abrupt transition in the radiation field incident upon the detector sometimes produces image artifacts in subsequent images. For example, in X-Ray detectors that use Thallium-doped Cesium-Iodide as the scintillator, the scintillation efficiency may be temporarily modified by the intensity of the incident X-Ray irradiation. Efficiency may be varied or changed across the collimator edge due to the gradiant of the incident X-Ray irradiation. When a subsequent X-Ray image is taken in a manner where the patient anatomy has been re-positioned over the effected region, the temporary change in the scintillation efficiency will cause an unwanted transition in the signal level across the boundary where the collimator was previously imaged. If this change in signal level (contrast) is greater than some fraction of the background image noise, this transition will be visible as an artifact. The artifacts typically are nuisance lines in the image that in the worst situations, obscure portions of anatomy that are diseased or injured. The obscuration can cause medical misdiagnosis or mistreatment of the anatomy.
Artifacts can occur in angioradiography applications, radiography extremity applications, and mammoradiography applications with high doses of X-Ray energy and with different sizes of collimation.
One conventional technique of correcting the artifacts is through a correction process in image-processing of the X-Ray system. However, the software-based correction requires considerable financial resources to develop and maintain.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a means to reduce artifacts in images that are caused by abrupt transitions in the strength of a projection of electromagnetic energy between areas of the projection, without use of software-base correction of the artifacts.